The present invention relates to the crimping of a filament yarn and more particularly to a process and an apparatus for crimping a filament yarn.
In recent years, in case of crimping a filament yarn, a so-called air stuffing crimping, which introduces a hot fluid entrained filament yarn into a stuffing chamber by use of a fluid jet nozzle, has been studied, because of its high-speed crimping and compactness of its apparatus.
According to the conventional methods of air stuffing crimping, high-speed crimping of filament yarn is possible, because the filament yarn is crimped efficiently by being plasticized with a hot fluid inside the hot fluid jet nozzle, and also by being subjected to hot fluid turbulence and then being stuffed into the stuffing chamber.
Moreover, the apparatus for air stuffing can be made very campactly with its stuffing chamber combined with a hot fluid jet nozzle.
However, in case of the above-mentioned process, it is very difficult to produce uniformly crimped yarn, because qualities of obtained crimped filament yarn, for example, crimp percentage, number of crimps, modulus of crimp, etc., are inclined to vary due to fluctuations occurring with the position of the stuffing start point (distance from the hot fluid jet nozzle to the filament yarn block already packed tightly in the stuffing chamber), stuffing density of filament yarn, releasing point, cooling of crimped filament yarn and so on.
From the above viewpoint, attmepts have been made to facilitate crimp fixing of filament yarn by the application of a cold fluid supplied into the stuffing chamber from an opposite direction, also of back pressure caused by the cold fluid on the filament yarn packed in the stuffing chamber (see U.S. Pat. No. 3802038, U.S. Pat. No. 3849844, Japanese Patent Application Laid-open No. 71242/74, Australian Pat. No. 74/76203, U.S. Pat. No. 3824656).
However, these processes are so composed as to let both the hot fluid and the cold fluid exhaust from the stuffing chamber, therefore it is difficult to keep the pressure balance between the hot fluid and the cold fluid under control, and any pressure unbalance thus occurring inevitably varies the position of the stuffing start point in the stuffing chamber, stuffing density, releasing point and so on.
In order to prevent these phenomena, means for controlling the pressure of both the hot and the cold fluid in said stuffing chamber has been proposed by providing a pressure control valve on the exhausting conduit of the stuffing chamber, but the system of this apparatus is complicated and unpractical (see U.S. Pat. No. 3802038, U.S. Pat. No. 3849844).